1. Field of the Invention
This invention relates to an improvement in a pressing machine of the type which comprises a press crank shaft which is rotatably supported by a housing and is adapted to be driven by a motor to rotate, a material feeding device which feeds a material in synchronization with the rotation of the crank shaft and is adapted to move toward and away from the crank shaft, and a torque transmission device which drivingly connects the crank shaft with an input shaft of the material feeding device.
2. Description of the Prior Art
One form of the conventional torque transmission device of the pressing machine described above employs endless transmission means such as a chain or a belt, while another type employs a gear and a shaft drive. However, in a wrapping connector driving type torque transmission device utilizing the endless transmission means, the operation may become impossible if the distance between two shafts is greatly varied because of the looseness of the chain or the belt. For this reason, a tension pulley is needed to adjust the degree of looseness during the operation. However, since this tension pulley is secured to a press housing or the housing of a material feeding device, it's use is limited in terms of the space needed for installation. Furthermore, the preset tension must be adjusted whenever the distance between the two shafts is changed. The synchronized relationship between the drive shaft and the follower shaft may deteriorate when the looseness of the belt or the chain is adjusted by means of the tension pulley. When the endless transmission means is employed, the side of the endless transmission means which is loose is determined by the direction of rotation of the pulley. Therefore, the tension pulley must be positioned on the loose side so as to be able to adjust this tension and it's position must be changed when the direction of rotation is reversed. As a result of this, the structure becomes complicated and the manufacturing cost is raised.
In a transmission device in which a gear and shaft drive are used, the transmission is conducted through a spline or a universal joint which is used for the purpose of adjusting the distance between the two shafts. In this type of the transmission device, however, backlash necessarily results, whereby the precision deteriorates, synchronization is not fulfilled, and the rotation becomes irregular. Further, it is necessary to provide a space for securing a gear box and the shafts to the housing or provide a space for the housing for supporting the same as in the case of the wrapping connector driving type transmission device. Furthermore, since the number of transmission elements from the driving side to the follower side is large, the time required for installing and detaching them is considerable.